The National Security Agency is reportedly collecting almost 5 billion cell phone records a day under a program that monitors and analyses highly personal data about the precise whereabouts of individuals, wherever they travel in the world.

Details of the giant database of location-tracking information, and the sophisticated ways in which the NSA uses the data to establish relationships between people, have been revealed by the Washington Post, which cited documents supplied by whistleblower Edward Snowden and intelligence officials.

The spy agency is said to be tracking the movements of “at least hundreds of millions of devices” in what amounts to a staggeringly powerful surveillance tool. It means the NSA can, through mobile phones, track individuals anywhere they travel – including into private homes – or retrace previously traveled journeys.

The data can also be used to study patterns of behaviour to reveal personal information and relationships between different users.

The NSA provided some input into the report, with one senior collection manager, granted permission to speak to the newspaper, admitting the agency is “getting vast volumes” of location data from around the planet by tapping into cables that connect mobile networks globally.

Civil liberties experts have long said that cell phone location data contains some of the most intrusive information about people in the digital age, leaving a kaleidoscopic footprint of a person’s life. Phones transmit location data whenever a phone is turned on, irrespective of whether they are being used to make calls or send text messages and emails.

According to the Post, the NSA is applying sophisticated mathematical techniques to map cell phone owners’ relationships, overlapping their patterns of movement with thousands or millions of other users who cross their paths.

These tools — known collectively as Co-Traveler — enable the NSA to search for possible associates of intelligence targets.

According to briefing slides cited in the report, the NSA draws location data from 10 so-called “sigads,” or signals intelligence activity designators, around the world, which in turn rely on data provided by corporate partners.

Defending the program, US officials told the Post that efforts to collect and analyze location data are lawful and intended strictly to develop intelligence about foreign targets, with information about the location of domestic cell phones only gathered “incidentally”.

Robert Litt, general counsel for the Office of the Director of National Intelligence, said: “There is no element of the intelligence community that under any authority is intentionally collecting bulk cell phone location information about cell phones in the United States.”

However, data is also gathered from the tens of millions of Americans who travel abroad with their cell phones every year, the Post reported.

“As with other surveillance activities, the NSA claims that its cell phone location program program is targeted at foreigners, and Americans' information is collected only ‘incidentally,’" said Elizabeth Goitein, a co-director of the Brennan Center’s Liberty and National Security Program.

“But the scale of foreign surveillance has become so vast, the amount of information about Americans ‘incidentally’ captured may itself be approaching mass surveillance levels.”

Two months ago, the director of the NSA, General Keith Alexander, admitted to secret pilot programs to monitor the precise location of Americans through their cell phones, saying the highly intrusive tracking data “may be something that is a future requirement for the country”.

He said in evidence to the Senate judiciary committee that pilot programs from 2010 and 2011 were intended to test the compatibility of the location data with the agency’s databases, but were not used for any intelligence analysis purposes.

It is not known whether or to what extent domestic spy agencies have dragnet collection programs for cell phone data, although the FBI does obtain such information through warrants in criminal investigations.

The latest disclosure comes at a point during which Congress is considering three separate bills that would to varying extents clips the wings of the NSA or reform the secret courts that intended to hold the agency to account.

None of the proposed reforms substantially alter the NSA's ability to surveil ordinary foreigners living outside of the US. The issue of surveillance of foreigners has mostly been low among the priorities of lawmakers, including those critical of the NSA, although there has been considerable concern raised about the agency monitoring the calls of leaders of allied nations.

Zeke Johnson, director of Amnesty International USA’s Security & Human Rights Program, said the latest revelations emphasized the need for Congress to take swift action. “Today's news is the latest startling blow to the right to privacy,” he said. “Congress should wake up from its post-holiday food coma and get to work passing legislation to reform the program.”

Catherine Crump, staff attorney with the American Civil Liberties Union's speech, privacy and technology project, had this said: “It is staggering that a location-tracking program on this scale could be implemented without any public debate, particularly given the substantial number of Americans having their movements recorded by the government.”